The growing interest in the intensity of light beneath the surface of the ocean from both the physical and the biological points of view has resulted in further efforts to obtain reliable measurements under widely differing conditions and in a variety of locations. For the most part, however, these measurements have been made in northern waters and have been confined largely to coastal regions. There has resulted a paucity of precise observations in the tropical parts of the ocean. The work of Grein (1913-14) in the Mediterranean produced highly irregular results (cf. Atkins, 1932). Certain visual observations have been made by Beebe (1934) off Bermuda, and a small number of measurements were undertaken by Stephenson (1934) from a submarine off California. The work of Hulburt (1932) was confined to measurements of the absorption coefficients of samples of sea water brought into the laboratory.